Comprehensive water treatment system

ABSTRACT

Disclosed is a novel helix drive for use with a valve assembly of a water softener. The helix drive comprises a stationary drive axle bearing a longitudinally slotted sleeve; a piston having an apertured end and being disposed within said drive axle sleeve; a transverse pin, having ends fitted with guide shoes, disposed through said piston aperture and located within said axle slot; and a drive gear having a pair of helix paths within said pin guide shoes are disposed. Rotation of said drive gear results in reciprocating longitudinal movement of the pin within the axle slot and, thus, the piston.

This application is a division of application Ser. No. 07/493,896, filedMar. 15, 1990, now U.S. Pat. No. 5,089,140 issued on Feb. 18, 1992.

BACKGROUND OF THE INVENTION

The present invention relates to water treatment systems, sometimescommonly known as water softening systems, and more particularly to aunique helix drive for use in a system comprising a water softeningunit, a control system therefor, and its use in commercial/industrialsettings.

Resin-type ion exchange devices have many uses, such as the softening ofwater. As the water to be processed is passed through the resin-filledtank, ions in the fluid to be processed, e.g. calcium, is exchanged withions found in the resin, e.g. sodium, thereby removing objectionableions from the water and exchanging them for less objectionable ionsfound in the resin. During this ion exchange process, the ability of theresin to exchange ions gradually is reduced. That is, the resin bedbecomes exhausted and, thereafter, water will flow therethrough inunprocessed form.

The capacity of the ion exchange resin bed can be determined from thevolume of resin used and the particular type of resin. The concentrationof contaminant(s) in the water to be processed can be determined, atleast on an average basis. Thus, the volume of water that can beprocessed by a particular water treatment unit is known. Once thatcapacity of water has been treated, the bed must be regenerated.

Regeneration of the ion exchange resins typically involves chemicallyreplacing the objectionable ions from the resin with less objectionableions, e.g. replacing calcium with sodium ions. This regeneration processrequires the suspension of the treatment process, thus necessitating thewater to by-pass the ion exchange resin tank. At the same time as theion exchange resin is regenerated, the bed can be backwashed in order toremove trapped particulate matter, the resin tank can be rinsed toremove objectionable soluble materials, an application of sterilizationagent to prevent bacterial growth can be accomplished, etc. All of theseoperations are known in the art.

In the regeneration of resin beds used to treat hard water, a variety ofcontrol modes have been employed commercially. For example, some watersoftening units function on a timer which necessitates regeneration atspecified time intervals. This mode of operation has the disadvantagethat the resin bed may have sufficient capacity remaining to continuefor quite a time thereafter. Another mode of control involves monitoringthe volume of water treated and provoking regeneration once a set pointhas been reached. Unfortunately, regeneration cycles can be triggeredundesirably at just the time when demand for water is high under thismode of operation.

One overriding consideration regardless of the mode of control employedinvolves exhaustion of the resin bed. If the resin bed is permitted tobecome completely exhausted of its capability of exchanging ions, asingle regeneration cycle will not be sufficient to establish theoriginal capacity of the bed. Instead, several regeneration cycles oftenwill be required. Moreover, if the bed is near its exhaustion point anda high demand for water is made, present commercial systems cannotprovide the capacity to soften the extra water demand without riskingtotal exhaustion of the resin bed. Accordingly, new water treatmentsystems including the mode of operation thereof are in demand in thisfield.

BROAD STATEMENT OF THE INVENTION

The present invention is a unique helix drive especially adapted for usein the novel valve assembly disclosed in U.S. Pat. No. 5,089,140, citedabove. The helix drive comprises a stationery drive axle bearing alongitudinally slotted sleeve; a piston having an apertured end andbeing disposed within said drive axle sleeve; a transverse pin, havingends fitted with guide shoes, disposed through said piston aperture andlocated within said axle slot; and a drive gear having a pair of helixpaths within said pin guide shoes are disposed, whereby rotation of saiddrive gear results in reciprocating longitudinal movement of the pinwithin the axle slot and, thus, said piston.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective elevational view of the ion exchange resinsystem including a cabinet which houses the ion exchange resin bed tankand the valve assembly;

FIG. 2 is a sectional view taken along line 2--2 of FIG. 1;

FIG. 3 is an elevational view of the components comprising the exchangemedium tank and their assembly;

FIG. 4 is a perspective view of the assembly of the valve body, pistonvalve assembly, injector assembly, and by-pass assembly;

FIG. 5 is a detailed drawing the novel helix drive, and of of thecomponents and their assembly for the injector assembly and valve bodyof FIG. 4;

FIG. 6 is a detailed drawing of the components and their assembly of thepiston valve assembly of FIG. 4;

FIG. 7 is a detailed drawing of the components and their assembly of thebypass assembly of FIG. 4;

FIG. 8 is a sectional view taken along line 8--8 of FIG. 1;

FIG. 9 is a side view of the helix drive components which providereciprocating longitudinal movement of the piston set forth in FIG. 8;

FIG. 10 is a cut-away view of the valve control assembly showing theflow of water and brine therethrough;

FIG. 11 is a flow diagram for the electronic control means used inconjunction with the water softening system of the present invention;

FIG. 12 is an alternative flow diagram to that set forth at FIG. 11; and

FIG. 13 is a schematic representation of a plurality of water softeningunits and their mode of operation in a single system.

These drawings will be described in detail in connection with thefollowing Detailed Description of the Invention.

DETAILED DESCRIPTION OF THE INVENTION

The water softening unit of the comprehensive water treatment systemdisclosed in U.S. Pat. No. 5,089,140 is depicted at FIG. 1. Housedwithin cabinet 10 is ion exchange medium tank 12. (See FIGS. 2 and 3).Mounted atop tank 12 is valve control assembly 14 which will bedescribed in detail in connection with FIGS. 4-9). Line 16 is forconnection to brine storage tank 18 and line 20 is the connection to adrain. Water enters the comprehensive water treatment system throughinlet 22 and softened water is withdrawn through outlet 24. Frame 26(see FIG. 2 also) mounts atop cabinet 10 and retains cover 28 whichhides valve control assembly 14.

While exchange medium tank 12 can be made in one or more sections, FIG.3 depicts it as formed from upper tank section 30 and lower tank section32. This arrangement permits the insertion of central annular sectionsto increase the height of tank 12 should it be necessary, desirable, orconvenient. Tank 12 is shown fitted with upper screen/distributor 34,center screen/distributor 36, and lower screen/distributor 38. The useof three screen/distributors as shown at FIG. 3 permits different resinsor exchange medium beds to be established between distributors 34 and36, and 34 and 38. Exchange beds also can be located atop distributor 34and beneath distributor 38, if necessary, desirable, or convenient. Itwill be appreciated that center screen/distributor 36 may be omitted toestablish a single bed. Alternatively, with additionalcentrally-disposed tank sections with associated screen/distributors,additional beds could be established as is necessary, desirable, orconvenient. Head space 35 is provided between upper screen/distributor34 and the spherical top of upper medium tank section 30. Preferably,head space 35 is filled with media (e.g. 60/80 mesh garnet) capable offiltering particulate contaminants from water passed therethrough.Mounting brackets 40 retain valve control assembly 14. Fill aperture 42in upper medium tank section 30 can be used to add resin to tank 12 forfilling the upper section housed within upper medium tank 30 and can beused for withdrawal of resin by inversion of tank 12. Fill plug 44 andO-ring 46 fill aperture 42 when access thereto is not required.Similarly, lower medium tank section 32 has drain plug 48 which retainslower fill plug 50 and O-ring 52.

Upper medium tank section 30 further has inlet aperture 54 and outletaperture 56 disposed about its spherical top. Flange 58 (see FIG. 2)projects downwardly from the top of upper medium tank section 30 andprovides communication between outlet aperture 56 and center flow tube60. Apertured plate 62 and associated O-ring 64 mate with flange 58 toprovide a cavity in communication with center flow tube 60 that fitsthrough the aperture in plate 62 and, thus, provide an outlet forsoftened water separate from the head space within upper medium tanksection 30 which is filled with service water to be softened as itenters tank 12 via inlet aperture 54. The flow of water admitted viainlet aperture 54 passes sequentially through the garnet media inheadspace 35 wherein particulate matter is filtered, through upperscreen/distributor 34 through upper resin bed 66, through centerscreen/distributor 36 and through lower resin bed 68, and finallythrough lower screen/distributor 38. The water then flows up throughcenter flow tube 60 and into the chamber created by flange 58 and plate62 for being withdrawn from tank 12 via outlet aperture 56.

Control of the flow of water between exchange medium tank 12, brinestorage tank 18, and within exchange medium tank 12 is controlled byvalve control assembly 14 which is depicted at FIG. 4. This assembly iscomposed of valve body 70, injector assembly 72, helix drive assembly74, and bypass assembly 76. This component and assembly drawing will bereferred to in connection with the detailed drawings of each of theseassemblies as depicted in other figures.

Referring to FIG. 5, valve assembly 70 and injector assembly 72 are seenin detail. Valve body 71 is seen to have eight ports: water inlet port78, softened water outlet port 80, helix drive port 82, drain port 84,first exchange medium tank port 86, second exchange medium tank port 88,first injector port 90, and second injector port 92. End cap 94, withO-ring 96 and cylinder insert 98 connects to flange 100, which retainsthreaded inserts 102a-102e, by bolts 104a-104e. Line 20 (FIG. 1)connects to end cap 94.

Injector assembly 62 is seen to be comprised of injector housing 106which has internally threaded end 108 into which fits throat 110, nozzle112, screen 114, O-ring 116, and threaded plug 118. Injector housing 106further has first ports 120 and second port 122. First injector port 120mates with first valve body port 90 with intervening O-ring 124therebetween. Second injector port 122 mates with second valve body port92 with O-ring 126 disposed therebetween. Threaded sleeve 128 isconnected to elbow 130 which serves as the brine tank port for injector72 and is connected to line 16 (see FIG. 1). Disposed within injectorhousing 106 and in the aperture formed by threaded sleeve 128 is spring132, poppet 134, and O-ring 136. This spring assembly is inserted intoinjector housing 106 via elongate aperture 138 and is sealed to theoutside by elongate cover 140 with intermediately disposed O-ring 142.Cover 140 is retained to injector housing 106 by threaded bolts144a-144f.

Referring to valve assembly 70, cylinder insert 144 (FIG. 5) fits intoaperture 82 which is surmounted by flange 146 which contains threadedinserts 148a-148e. Valve assembly 150 is comprised of piston 152 whichretains first valve 154 and second valve 156. One end of piston 52 isterminated by crucifix 158 which fits into valve body end cap 94 and isterminated at the other end by transverse aperture 160. Drive axle 162bears longitudinally slotted sleeve 164 and has mounts for mountingmotor 166 with screws 168a and 168b. Drive axle 162 itself is mounted tovalve body flange 146 by bolts 170a-170e. The apertured end of piston152 fits through drive axle 162 and slotted sleeve 164. Cross pin 172with guide shoes 174 and 176 fits through aperture 160 and rides in thelongitudinal slot in slotted sleeve 164. Slotted sleeve 164 permitspiston 152 to move in a longitudinal direction only.

The helix drive unit (FIG. 6) that provides reciprocating movement ofpiston 152 includes bushing 178, helix drive gear 180, helix drivecenter 182, and helix drive end 184. Switch ring double 186, switch ringsingle 188, and bushing thrust washer 190 complete the helix driveassembly. Referring to FIG. 4, motor cover 192 attaches to the motormount flange of drive axle 162 with screws 194a and 194b. Junctionprinted circuit board (PCB) 196 similarly is attached with screws 198aand 198b. O-ring 200 completes the waterproof seal established betweenhelix drive assembly 74 and valve body 70.

Referring now to bypass assembly 76 depicted in detail at FIG. 7, bypasshousing 202 has water inlet port 204 that connects to valve body inletport 78 and water outlet port 206 that connects to valve body outletport 80. O-rings 205 and 207 seal port 204 to valve body inlet port 78and port 206 to valve body outlet port 80, respectively (see also FIG.4). Turbine 208 is retained in port 206 by flow director 210. Mounted inconjunction therewith is pressure differential switch 212, mounted withscrews 214a-214d and O-rings 216a and 216b, and turbine sensor PCB 218retained by sensor cap 220 and screw 222. Switch 212 permits thepressure drop across the resin beds to be monitored based on the inletand outlet water pressures. If this value is too great, likely the resinbed(s) is clogged and the water softening system is shut out, i.e. fullby-bass mode is established. The turbine sensor assembly provide flowmetering of the softened water exiting the system. Full bypass of wateris achieved using bypass assembly 76 by activating rotating handle 224which is affixed to bypass housing 202 by screw 226. Handle 224, inturn, is attached to drive shaft 228 which accommodates O-ring 230therebetween. Drive shaft 228, in turn, screws into piston assembly 230which is connected at its other end to end cap 232. End cap 232, inturn, retains valve test port 234. End cap 232 is attached to bypasshousing 202 by screws 236a-236h which screw into threaded inserts238a-238h which are retained by bypass housing 202. O-ring 240 completesthe seal established between end cap 232 and bypass housing 202.

Finally, O-rings 242 and 244 provide sealing engagement between firstand second tank ports 86 and 88, and inlet 54 and outlet 56,respectively, of upper medium tank section 30. Injector assembly 72 isaffixed also to upper medium tank section 30 by screws 246a and 246b.Bypass housing 76 is retained by screws 248a-248c. Thus, completes theassembly of valve control assembly 14.

As to operation of valve control assembly 14, reference is made to FIGS.8-10. Piston valve assembly 150 disposed within valve body 70 has threedistinct positions to which valves 156 and 154 are brought. Junction PCB196 in conjunction with switching 186 and 188 provides a stopping pointwhen each of these three positions is reached and, thus, permits motor166 to be deactivated, as will be more particularly described below. Theposition of piston valve assembly 150 depicted in FIG. 8 is the normaloperational mode wherein service water to be softened enters valve body70 via inlet port 78 and passes through second tank port 88 into tank 12to be softened. Valve 154 is in contact with valve seat 252 and, thus,prevents the water from flowing past first valve 154. Similarly, drainline 20 is blocked by O-ring 230 at the crucifix end of piston 152.Softened water is withdrawn from exchange medium tank 12 via first tankport 86 and out of valve body 70 via outlet port 80, first valve 154again preventing the water from flowing therepast due to its seatingagainst valve seat 252. In this normal operational mode, second valve156 performs no function. Motor 166 causes center helix drive 182 torotate its valve actuating surface (e.g. by camming action) into contactwith poppet valve 134 to open elbow 130 and permit softened water toflow out threaded sleeve 128, elbow 130, into line 16, and finally intobrine storage tank 18. All brine created in tank 18 is with softenedwater. Next, motor 166 drives piston 152 to a position whereat secondvalve 156 seats against valve seat 250. This opens drain line 20. Firstvalve 154, however, still is in contact with valve seat 252. The newposition of second valve 156 prevents service water entering valve bodyinlet port 78 from flowing to valve body second tank port 88. Instead,the position of first valve 154 permits service water to now flow outvalve body second injection port 92 and thence into injector housing106. A portion of the water also flows out injector first port 120 intovalve body 70 and out valve body first tank port 86 into exchange mediumtank 12, but in the direction opposite the normal flow establishedduring softening of inlet service water. This is the so-called"backwash" that is conventionally known in the art. The backwash cyclepermits suspended solids and foreign matter to be washed from the garnetbed and ion exchange resin housed within exchange medium tank. Thisbackwash of water passes through valve body second tank port 88 and outdrain line 20. Double switch ring 186 and single switch ring 188 permittiming by the controls for the duration of all cycles by carrying seventhree-bit binary numbers that provide feedback to the microprocessorestablishing the precise position of piston 152 and, hence, the precisecycle and flow of water in valve control assembly 14. Detents inswitchings 186 and 188 engage switches on junction PCB 196 and form thebinary number, though lands or other indicia could be used.

When this cycle has been completed, piston 152 again traverses to aposition whereat second valve 156 still retains contact with valve seat250, but now first valve 154 is seated against valve seat 254. In thisposition, the flow of service water entering valve body inlet port 78and out valve body second injection port 92 is of such a sufficientvelocity as it passes through nozzle 112, that a partial vacuum isestablished within injector housing 106 in communication with threadedsleeve 128. Poppet 134 is moved to an open position by the cammingaction of drive 182 so that this partial vacuum sucks brine water frombrine tank 18 back through line 16 and into injector housing 106 to bemixed with service water passed through injector first port 122 intovalve body 70 and thence out valve body first tank port 86. This"brining" or reverse ion exchange refreshes the ion exchange resin andrestablishes its initial capacity for softening water. The effluent iswithdrawn from exchange medium tank 12 through valve body second tankport 88 and out drain line 20. Again, when the timer indicates that thiscycle has been completed, piston 152 reciprocates in the oppositedirection and each of these operations sequentially is conducted again,but now in the reverse order. That is, at the next or middle position,the ion exchange resin is backwashed. Thereafter, piston 152 is movedback to the position depicted at FIG. 8 and water softening isrecommenced. Finally, softened water again is permitted to flow intobrine storage tank 18. During the brining operation, a flow of waterdirectly between valve body inlet port 78 and outlet port 80 isestablished so that no loss of service is experienced.

The reciprocating movement of piston 152 is determined by helix driveassembly 74, particularly as it relates to helix drive gear 180, helixdrive center 182, and helix drive end 184. Referring more particularlyto FIG. 9, it will be observed that guide shoe 176 is disposed in thehelix path canted in one direction. Not shown in FIG. 9 is guide shoe174 that is disposed opposite guide shoe 176. These guide shoes followthe double helix path. Since, however, cross pin 172 has only one degreeof freedom of movement, viz. in the slot of slotted sleeve 164, crosspin 172 guided by guide shoes 174 and 176 can only move longitudinallyin the direction of piston 152 as the helix drive rotates powered bymotor 166. A simple, yet highly efficient and reliable reciprocatingmotive system for piston 152, thus, is disclosed.

The operation of valve control assembly 14 is controlled by amicroprocessor that contains a program that will be described below inconnection with FIG. 11. Initially, however, data must be entered intothe program in order to calculate the RESERVE for the system. The watertreatment system of the present invention maintains a reserve capacityin order to prevent the resin bed from becoming completely exhausted.Preferably, this reserve is equal to one day's average use of water,though other time periods can be selected as is necessary, desirable, orconvenient. In order to calculate the RESERVE, the "grain capacity" ofthe resin tank must be entered (this is dependent upon the quantity ofresin in the tank and the composition of the resin), the hardness of thewater to be treated is entered; the number of people in the family beingserved by the water treatment system is entered; the average consumptionof water, gallons/day, is embedded in the software, though it could be avariable which also is entered; and the computer then calculates theRESERVE. As an example, assume that the capacity of tank 12 is 23,000grains, the hardness of the water to be treated is 10 grains/gallon, thefamily comprises four persons, and the average comsumption is 75gallons/day/person. The total capacity of tank 12 is 2300 gallons andone day's RESERVE is equal to 300 gallons. The volume of water intendedfor softening prior to regeneration, V_(s), then is equal to 2,000gallons. The time of day that the computer samples the status of thesystem additionally can be a variable, or it can be preset in thecomputer, e.g. conveniently to 12 o'clock p.m.

With the foregoing information entered into the computer, the computerprogram starts at block 256. Since the system is designed to preventcomplete exhaustion of the resin bed in tank 12, the initial step of thecomputer program at block 258 looks to see whether the volume of watersoftened exceeds the calculated capacity, V_(s), of the resin bed(s) intank 12. In the hypothetical set forth above, the capacity has beencalculated to equal 2,000 gallons. If the program determines that thiscapacity has been exceeded, the program proceeds to block 260 whereinregeneration of the resin bed is commenced immediately, regardless oftime of day. The computer program at block 261 also looks to see thepressure differential, P, between the incoming hard water and theoutgoing softened water. If P exceeds a given value for the system, itis assumed that the resin beds are clogged and emergency regenerationalso is required. The regeneration of the resin bed is accomplished withthe water treatment system as described in connection with the previousdrawings. These are override situations that occur at blocks 258 and 261in the program and are unique features of the present invention.

If the volume of water softened, V_(s), has not exceeded the capacity ofthe system and the pressure differential has not exceeded the targetvalue, the computer program proceeds to block 262 wherein the time ofday, T_(d), is sampled. As noted above, this time can be set by theuser, or can be embedded in the computer program. Midnight is aconvenient time for sampling the system since it is a likely time thatno water demand is made on the water treatment system. If the set timeof day has not been reached, then the program returns to block 258. If,however, the sample time of day has been reached, then the computerprogram continues to block 264 wherein the program again looks to seewhether the design capacity of the system, viz 2,000 gallons in theexample above, has been reached. In other words, the program looks tosee whether the water treatment system has entered the RESERVE capacityset for the resin bed. If this value has not been reached, then theprogram returns to block 258.

If the program determines that the resin bed is operating in the RESERVEportion of the bed, then the computer program continues to block 266wherein the computer calculates the volume of water required to be addedto brine storage tank 18 in order to make sufficient brine to regeneratethe resin bed and re-establish its initial capacity. Since the volume ofwater passed through the resin bed can vary, this step of the computerprogram ensures that only the minimum amount of brine required toexchange with the resin bed is used. Since the regeneration sequence ofthe present invention always retains a fraction of the brine preformedin brine storage tank 18, only the volume of water needed to bring thebrine up to the required volume needs to be added. Once the volume ofwater is calculated at block 266, the computer program proceeds to block268 wherein motor 166 is actuated for rotating the helix drive so thatthe camming action of center helix drive 182 activates poppet 134 topermit the computed volume of water to flow into brine storage tank 18.Next, motor 166 is actuated for moving piston 152 disposed in valve body70 to backwash the resin in exchange medium tank 12. The program thenproceeds to block 270 wherein a time pause or delay, T_(p), isencountered. This delay permits sufficient time for the water passedinto brine storage tank 18 to dissolve sufficient brine to establish abrine solution adequate for treatment of the resin in exchange mediumtank 12. A conventional time pause is two hours, which means that theregeneration of the resin bed normally will occur at 2:00 a.m. inaccordance with step 272 of the computer program. It will be observedthat under the emergency regeneration mode of operation at block 260,the time pause at block 270 also is encountered. Following regenerationof the resin bed, the program proceeds to step 274 wherein theaccumulated volume of water softened is reset to zero. The program thenreturns to block 258 of the program.

The emergency regeneration carried out at block 260 of the computerprogram calls for the bed to be regenerated with the brine present inbrine storage tank 18 by virture of refill No. 1. Following this partialregeneration of the resin bed, refill No. 1 is set for the full capacityof the resin bed and refill No. 2 is omitted. At T_(d), the full amountof brine in brine storage tank 18 then is used to regenerate the bed.Depending upon the amount of water that has been used between the timeat which the emergency regeneration was executed and the normalregeneration time, T_(d), this sequence under emergency regeneration mayresult in the overbrining of the bed. Alternatively, an extra demand ofwater thereafter could result in the capacity of the resin bed beingexceeded again before reaching the appropriate standard regenerationtime of day, T_(d). Accordingly, the alternative computer programdepicted at FIG. 12 modifies the emergency regeneration sequence.Following the emergency regeneration at step 260, the program proceedsto block 276 wherein the volume of water softened again is monitored tosee whether it has exceeded the capacity of the system, viz 2300 gallonsin the example used herein. If this capacity again has been exceeded,then the program returns to step 260 wherein emergency regenerationagain is executed. If, however, the full capacity of the resin bed hasnot been exceeded, the computer program continues to block 278 whereinthe time of day again is sampled. This time of day may or may not be thesame time that standard regeneration at block 262 utilizes. If thissample time of day at block 278 has not been reached, then the programreturns to block 276 for monitoring the capacity of water passed throughthe water treatment system again. If the sample time of day has beenreached, then the program continues to step 280 wherein valve controlassembly 14 is activated for filling brine storage tank 18 withsufficient water to completely brine the resin bed and the programcontinues to block 270.

When a plurality of the comprehensive water treatment systems are to beused in a commercial or industrial setting wherein large capacities ofwater need to be softened, the operational sequence as illustrated atFIG. 13 may be used. Merely for illustrative purposes, five units werechosen to be depicted at FIG. 13. It will be appreciated that a greateror lesser number of units may be combined in parallel operation asillustrated at FIG. 13. Again, it is mandatory that none of the unitshave a quantity of water passed therethrough so that the resin bed iscompletely exhausted. Since no two water treatment units will expressthe same pressure differential thereacross, and hence the samevolumetric flow of water, it is not safe to assume that one-fifth of theflow of water will be passed through each of the five units when theyare operated in parallel. If this assumption were made, the operatortakes a definite risk that one of the units will preferentially exhibita lower pressure differential thereacross and, hence, it could beoperated to exhaustion. Thus, this operational mode of the presentinvention always ensures that no tank will be depleted. As analternative, the regenerated tank, for example, could be held off-linewhich would provide at least one tank in reserve should an emergencysituation arise.

With the four water softening units illustrated at FIG. 13 at the top,each unit starts with a complete resin bed as illustrated at A. Fiveregeneration cycles then are depicted at C-G. In order to establish thesequence for the meter demand set point, the capacity of the smallest ofthe four units is divided by the number of units. In the illustration atFIG. 11 with equal capacity units, the capacity of any one unit would bedivided by four. Say, that each unit is capable of softening 120 gallonsof water. This capacity divided by the number of units makes the setpoint at 30 gallons. This means that units 1-4 on the average willsoften each 30 gallons. One or more of the units may be above or belowthis average figure. When this capacity has been first reached by any ofthe units, unit 1 then is regenerated. The choice of tank 1 isarbitrary. Any unit could have been selected, not necessarily the unitthat triggered regeneration. When unit 1 has been regenerated, it isimmediately placed back in service. The counter is reset to zero at theonset of regeneration. Monitoring of when any unit reaches 30 gallonsagain is commenced. At cycle D when 30 gallons again is first reached byany unit, sequentially tank 2 is regenerated and the remaining unitscontinue to soften the water. By the time that cycle E is reached, theonly unit not to be regenerated, unit 4, has run through four cycles ofwater softening. Since on the average each cycle involves the softeningof 30 gallons, its capacity has not been reached and at cycle F, it iswithdrawn for regeneration. The cycle then commences again at G. Whilethis example is based on 4 units, it will be understood that othernumbers could be used to calculate the regeneration set point. Ofimportance is the operation in a mode whereby complete exhaustion of anyone unit is avoided. By basing regeneration on the smallest capacityunit, uneven capacity units also can be used as is necessary, desirable,or convenient.

We claim:
 1. A helix drive for a piston which comprises:(a) a stationary drive axle bearing a longitudinally sleeve having a slot therein; (b) a piston having an end having an aperture therein and being disposed within said drive axle sleeve; (c) a transverse pin, having ends fitted with guide shoes, disposed through said piston aperture and located within said axle slot; and (d) a drive gear having a pair of helix paths within which said pin guide shoes are disposed, whereby rotation of said drive gear results in reciprocating longitudinal movement of said pin within said axle slot and, thus, said piston. 